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MICROCOPY RESOLUTION TEST CHART
NATIONAL QUREAU OF STANDARDS - 1963


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CORNUD,3204
CONF-670534-3
MASTER HP
ELECTRON SPECTROMETRY OF DOUBLE-ELESTRON EJECTION FROM RARI
27
GAS ATOMS IN THE PHOTOABSORPTION PROCESS*
CESTI PRICES
Manfred 0. Krause
Oak Ridge National Laboratory
A
In the common photoelectric effect the photon hv imparts the kinetic energy
E = hv - IL
(1)
to an electron with the binding energy Ij. In the double-photoelectric effect two elec-
trons share the energy according to
Ez + Ez = hy - Iz - Iz
where Iz is the energy required to ionize the second electron.
. When orbital electrons are ejected by monochromatic x rays of energy hy, the elec-
trons will produce an energy spectrum which exhibits a) one discrete line characteristic
of single electron emission (
discrete lines due to excitation of a second
electron (Fq. ¿ with Ez = 0 and Ia → Eexcitation), and c) continuous distribution li Ez)
and f(E2) due to the emission of two electrons.
In this study we shined x rays from suitable targets on various rai
analyzed the emitted electrons with an electrostatic energy analyzer. We scanned the
discrete line spectrum and the continuous spectrum that contains the more energetic of
the 'Wo emitted electrons, i.e., f(E2): (f(EL) is complementary to f(E2); Cf. Eq. 1).
Figure 1 shows a typical spectrum for the photoabsorption of Mg Ka x rays in neon.
At AE = - + 2) eV, measured from the photoline (single electron process), a line
appears which indicates the excitation 2p 3p of a second electron in a monopole transi.
tion; at AE = -( 42 + 3) eV a cor.' inuous spectrum begins which indicates the simultaneous
emission of an L electron and a K electron. The inset of Fig. 1 gives the spectrum f(E2)
which is obtained after subtracting the average background and the spectrum arising from
inelastic energy losses in collisions with neutral gas atoms. From spectra of the kind
of Fig. 1, we have derived for various systems hy + A, A = He, Ne, and Ar, probability
values of double electron emission, probability values of ionizing one electron and exci-
ting another, energy values of I, and Eexcitation, and energy distributions of the elec-
Lectron process. In Table I we summarize the major results,
namely the probabilities of removing two electrons from their orbitals.
Table I. Probabilities of Double-Electron Interaction of Photons
(In Percent)
Ionization
Exptl.: Theory
Excitation
Expti. Theory
Shells
Total
Exptı. Theory
Ne KL
16.5
.
Ar KL
Ar KM
18.5
2.5
21.2
18.18
2.08
20.58
1
la i Mo i i
VI 1
18.2
.
T
..
.
He KK
1.89/6.36
1²/3.70
13
Ne LL
< 24
~ 26
4.58
Pr MM
26
1r
T-
STS
1
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:
BLANK PAGE
14
F
trong ata 1 42 tinguen a continuous spectrum beging which indicates the simultaneous
mission of an L electron and & K electron. The inset of Fig. I gives the spectrum f(ES)
which is obtained after subtracting the average background and the spectrum arising from
inelastic energy losses in collisions with neutral gas atoms. From spectra of the kind
of Fig. 1, we have derived for various systems hv + A, A = He, Ne, and Ar, probability
values of double electron emission, probability values of ionizing one electron and exci.
ting another, energy values of. Iz and Eexcitation, and energy distributions of the elec-
trons emitted in the two-electron process. In Table I we summarize the major results,
namely the probabilities of removing two electrons from their orbitals.
Table I. Probabilities of Double-Electron Interaction of Photons
Excitation
(In Percent)
Ionization
Expti. . Theory
Total
Expti. Theory
Shells
Expti.
Theory
Ne KL
2
16.5
18.5
.
18.
2.08
Ar KL
2.5
Ar KM
3
18.2
21.2
20.52
He KK
1.8*/6.36
< 10/3.70
13
Ne LL
4.58
< 10
~ 10
vi ?
Ar MM
16
~ 26
3.ga
Shakeoff theory, see Refs. 2 and 4
1) Electron correlation considered., see Ref. 5 (1sa → Co, 2s only)
c) Electron correlation considered, see Ref. 6
*Research Sponsored by the U.S. Atomic Energy Commission under contraint with the
Union Carbide Corporation.
DISTRIBUTION OF THIS DOCUMENT, IS UNLIMITED
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These data can be placed into two categories:
A) Electrons coming from shells of different principal quantum numbers, for example:
KL of Ne and Ar, and KM of Ar.?
B) Electrons originating from the same shell, for example: KK of He, and the outer
shells of Ne and Ar..
This classification is based on the theoretical interpretation of the data. As seen
from Table I the observed intensities of double-electron ejection are well accounted for
by the theory of electron shakeofft if the electrons come from different shells. The
same theory gives also a fair representation of the energy distribution of the continuum
electrons, it widerestimates, however, the probability of two-electron interactions, when
the electrons originate both from the outer shell. In such cases, we suspect, the inter-
action of the two electrons in question, commonly known as electron correlation, should
be considered in calculating the matrix elements for the transitions. Indeed, inclusion
of correlation effects has been shown.go to lead to good agreement between theory and
experiment for the photo-excitation and photo-ionization of He.
ude we may point out that multiple ionization phenomena are very sensitive
probes of the details of atomic structure. Observation of the electrons emitted, as done
in this experiment, offers direct and specific information which is needed for further
refinement of existing theories.
REFERENCES
1. M. O. Krause, Phys. Rev. 140, A1845 (1965); Phys. Letters 19, 14 (1965).
This work shall be submitted to Phys. Rev. for publication. See also M. O. Krause,
T. A. Carlson and R. K. Dismukes, Bull. Am. Phys. Soc. 11, 353 (1966), and M. O.
Krause and T. A. Carlson, Bull. Am. Phys. Soc. 11., 818 (1966).
3.
T. A. Carlson, Phys. Rev. 156, 142 (1967).
The sudden change in atomic potential by the fast removal of an inner electron nay
cause excitation or ionization of another electron, especially an outer electron.
See, for example, T. A. Carlson and M. O. Krause, Phys. Rev. 140, A1057 (1965), where
further references are cited.
5. E. E. Salpeter and M. H. Zaidi, Phys. Rev. 125, 248,(1962).
6. F. W. Byron, Jr., and C. J. Joachain, Phys. Rev. Letters 16, 1139 (1966); Phys. Let-
ters 24A, 616 (1967).
LEGAL NOTICE
This report mo prepared u an account of Government sponsored work. Neither the United
dutos, por the Commission, nor any person acting on behalf of the Commission:
A. Nakos any warranty or representation, expressed or implied, with ruspeat to the accu-
racy, coinplateness, or unetuloon of Ibo Information contained in this report, or that the wo
of any lafo::xawon, appu atus, method, or procon dircional la thulo report may not infringe
privitonwood rights; or
B. Arrumar any liabilities with respect to the one of, or for damages resulting from the
un of aay Information, appuntui, motbod, or proceu discloud in the report. ...
As und in the abovo, "peria acting on behalf of the Commission" Includes any om-
ployw or contractor of the Commission, or employu of such contractor, to the extent that
guch employs or contractor of the Commission, or employw of ench coatructor properes,
dienominatai, or provides sccuu to, may Information pursuant to Me employmeat or contract
with the Commission, or his employment with such contractor,
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ORNL-DWG 66-3822R
1400

Nek (MgK.) = 386.9 eV
1200
1000
1s2s22p5
– IONIZATION LIMIT —
ENERGY SPECTRUM
OF COMPLEMENTARY
SHAKEOFF ELECTRONS
BOUND
STATES
UNCORRECTED
p+3p
counts in 22 min
M L 8 1.4%
450
120 80 40
AE, ENERGY LOSS (EV)
---- INELASTIC SCATTERING
LOSSES
------ AVG BG
NeL2,3/CK)
__NELq(CK)
Nek
(MgKaz)
Nek
(Mgkan
Vendor logget
hot boo 1.
-
--
Tom
20
40 60
HANNEL NUMBER
80
100
Photoelectron Peak Nek(Mg Ka) and Satellite Distribution due
to Shakeoff of an L Electron.
Fig 1.
BT
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END

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